One solution requires constraining communication to proceed by round: each
process repeatedly broadcasts a message with its current round number, waits
for as many messages as possible bearing this round number, and changes
round by computing both its next state and its next message. Among the
formalisms that abstract round-based models, we consider the Heard-Of model
of Charron-Bost and Schiper [1]}; it boils down the
communication model to a description of all accepted combinations of
received messages. Formally, this is done by considering communications
graphs, one for each round, and taking the sets of infinite sequences of
graphs that are allowed by the model. Such a set is called a heard-of
predicate, and captures a communication model.
